Graphene quantum dots (GQDs) are single atom thick sheets of graphene that generally have no dimension greater than 100 nanometers (nm). GQDs can be used in a wide variety of applications ranging from electronics, optoelectronics and electromagnetics. The electrical, magnetic, optical and chemical properties of GQDs are governed by their size and edge crystallography. Compared to graphene, GQDs exhibit stronger photoluminescence useful in bioimaging, biosensing and light-emitting diodes.
A number of methods have been developed to synthesize GQDs. These methods generally fall into two groups: “top-down” and “bottom-up” methods. In top-down methods, larger carbon materials such as carbon nanotubes, graphene sheets and carbon fibers are cut to form the smaller GQDs. In bottom-up methods, GQDs are fabricated from smaller carbon precursors. Glucose, hexa-peri-hexabenzocoronene and citric acid have been used to form GQDs using bottom-up methods. However, bottom-up methods in current use require harsh, time consuming and/or complicated conditions, which include the use of strong acids and alkali, long treatment times and separation processes.